Composite construction and manufacturing method thereof

ABSTRACT

A composite construction  1  is obtained by coating the outer periphery of a core material  2  with a shell layer  3.  The core material  2  is composed of a first sintered body that is obtained by bonding, with a binder metal, a first hard particle composed of one or more of carbides, nitrides and carbonitrides of metals of Groups 4a, 5a and 6a of the Periodic Table, or a first ceramics obtained by bonding, with a sintering additive, a first ceramic particle composed of at least one of oxides, carbides, nitrides and carbonitrides selected from the group consisting of metals of Groups 4a, 5a and 6a of the Periodic Table, Al, Si and Zn. The shell layer  3  is composed of a second hard sintered body or second ceramics having a different composition from the first hard sintered body. The ratio of the residual free carbon amount C in  in the core material  2  to the residual free carbon amount C out  in the shell layer  3,  C in /C out , is 0.5 to 2. This prevents shrinkage during the time of sintering and also prevents the strength of the composite construction from lowering due to poor sintering.

FIELD OF THE INVENTION

[0001] The present invention relates to a composite constructionobtained by coating the outer periphery of a core material with a shelllayer having a different composition from the core material, as well asa method of manufacturing the same.

BACKGROUND OF THE INVENTION

[0002] Conventionally, there has been studied a technique of improvingthe toughness of a construction in addition to its hardness and strengthby coating the outer periphery of a continuous core material, such asfabrics, with other material. For example, U.S. Pat. No. 5,645,781describes that a composite construction excellent in toughnessindicating non-brittle fracture characteristic is obtainable bystretching by co-extrusion a laminated molding in which the outerperiphery of a cylindrical core material molding composed of a firstceramic powder containing a large amount of organic binder(thermoplastic polymer) is surrounded by a shell layer moldingconsisting of a second ceramic powder different from the ceramic powderof the core material and an organic binder, and then sintering thestretched molding.

[0003] However, in the composite construction obtained by the methoddisclosed in U.S. Pat. No. 5,645,781, it is necessary to add a largeamount of organic binder in order to perform co-extrusion molding.Therefore, during the time of sintering, a large amount of the organicbinder are decomposed and volatilized, thereby forming voids. A largeburning shrinkage occurs when these voids are eliminated for densifyingthe construction during the time of sintering. As the result, in thecomposite construction obtained by sintering, a large residual stressoccurs between the core material and shell layer. In some cases,delamination between the two is facilitated and the strength of thecomposite construction decreases.

[0004] Further, with the above method, it is necessary to decompose andvolatilize a large amount of the organic binder. In practice, binderburnout treatment has a limitation. Particularly, when there is a largeamount of the organic binder remaining without being decomposed andvolatilized, i.e., residual free carbon, in the core material located atthe inside of the composite construction, the core material suffers frompoor sintering and its sintered density does not increase, thusdeteriorating the strength of the composite construction.

SUMMARY OF THE INVENTION

[0005] It is a main object of the present invention to provide acomposite construction exhibiting excellent strength, hardness andtoughness even when molding and sintering are performed by adding inparticular a large amount of organic binder, as well as a method ofmanufacturing the same.

[0006] It is another object of the present invention to provide acomposite construction capable of efficiently performing binder burnouttreatment even when molding and sintering are performed by adding alarge amount of organic binder, as well as a method of manufacturing thesame.

[0007] The present inventors considered the above problem and found thefollowings. In the case of reducing the amount of excess residual freecarbon remaining in a core material, it is possible to reduce the amountof shrinkage occurred when sintering the core material and reduce theresidual stress between the core material and shell layer. Thiseliminates delamination and residual stress occurred between the corematerial and shell layer, thereby providing a composite constructionexcellent in hardness, toughness and strength.

[0008] In the present invention, a first method for reducing the amountof carbon remaining in a core material is that the same metal powder asa metal composition of a first hard particle or first ceramic particleis added to the raw material of the core material, and during the timeof sintering, the metal powder is allowed to react with the residualfree carbon remaining as a residue of an organic binder, in order togenerate a metal carbide.

[0009] A second method for reducing the amount of carbon remaining in acore material is that an oxide powder that changes to a hard particle orceramic particle of carbide, nitride or carbonitride is added to the rawmaterial of the core material, and during the time of sintering orbefore sintering, the oxide powder is subjected to carbonization orsubjected to carbonization and nitriding in order to release oxygen, andthen allowed to react with the residual free carbon remaining as aresidue of an organic binder. A third method for reducing the amount ofcarbon remaining in a core material is that an iron family metal oxidepowder is added to the raw material of the core material, and during thetime of sintering or before sintering, the iron family metal oxidepowder is subjected to reduction in order to release oxygen, and thenallowed to react with the residual free carbon remaining as a residue ofan organic binder. A composite construction excellent in hardness andtoughness and also excellent in strength is obtainable because the oxidepowder can be changed to a carbide, nitride, or carbonitride, eachhaving a higher hardness.

[0010] The composite construction of the present invention obtainedbased on the above-mentioned first method includes a continuous corematerial composed of a first hard sintered body or first ceramics, and ashell layer that coats the outer periphery of the core material and iscomposed of a second hard sintered body or second ceramics having adifferent composition from the first hard sintered body and firstceramics. The ratio of the residual free carbon amount C_(in) in thecore material to the residual free carbon amount C_(out) in the shelllayer, C_(in)/C_(out), is 0.5 to 2. Here, the first hard sintered bodyis obtained by bonding, with a binder metal, a first hard particlecomposed of at least one selected from carbides, nitrides, andcarbonitrides of metals of Groups 4a, 5a and 6a of the Periodic Table.The first ceramics is obtained by sintering, with a sintering additive,a first ceramic particle composed of at least one of oxides, carbides,nitrides, carbonitrides and borides selected from the group consistingof metals of Groups 4a, 5a and 6a of the Periodic Table, Al, Si and Zn.

[0011] The residual free carbon amount C_(in) in the core material ispreferably not more than 1% by weight. It is desirable that the samemetal as the metal composition constituting the first hard particle orfirst ceramic particle is present in the core material. It is alsodesirable that the tensile stress on the core material surface is notmore than 200 MPa. In an alternative, a plurality of the above-mentionedcomposite constructions may be bound to obtain a construction having amulti-filament structure.

[0012] The composite construction of the present invention obtainedbased on the above-mentioned second method includes (i) a continuouscore material composed of a first hard sintered body obtained bybonding, with a binder metal, a first hard particle composed of at leastone of carbides, nitrides and carbonitrides, which are obtained byperforming carbonization and/or nitriding of at least one oxide selectedfrom the group consisting of metals of Groups 4a, 5a and 6a of thePeriodic Table, Si, Zn and Sn, or a first ceramics obtained by boding,with a sintering additive, a first ceramic particle composed of at leastone of carbides, nitrides and carbonitrides, which are obtained byperforming carbonization and/or nitriding of at least one oxide selectedfrom the group consisting of metals of Groups 4a, 5a and 6a of thePeriodic Table, Al, Si and Zn, and (ii) a shell layer that coats theouter periphery of the core material and is composed of a second hardsintered body or second ceramics that has a different composition fromthe first hard sintered body.

[0013] Alternatively, the composite construction of the presentinvention based on the above-mentioned second method includes (i) acontinuous core material composed of a first hard sintered body obtainedby bonding, with a binder metal, a hard particle in which at least oneoxide selected from the group consisting of metals of Groups 4a, 5a and6a of the Periodic Table, Si, Zn and Sn, is mingled with at least one ofcarbides, nitrides and carbonitrides, or a first ceramics obtained byboding, with a sintering additive, a first ceramic particle in which atleast one oxide selected from the group consisting of metals of Groups4a, 5a and 6a of the Periodic Table, Al, Si and Zn, is mingled with atleast one of carbides, nitrides, carbonitrides and borides, and (ii) ashell layer that coats the outer periphery of the core material and iscomposed of a second hard sintered body or second ceramics that has adifferent composition from the first hard sintered body.

[0014] The composite construction of the present invention based on theabove-mentioned third method includes (i) a continuous core materialcomposed of a first hard sintered body obtained by bonding, with abinder metal composed of an iron family metal obtained by reducing anoxide, a first hard particle composed of at least one of carbides,nitrides and carbonitrides of at least one selected from the groupconsisting of metals of Groups 4a, 5a and 6a of the Periodic Table, Si,Zn and Sn, or a first ceramics obtained by boding, with a sinteringadditive containing an iron family metal obtained by reducing an oxide,a first ceramic particle composed of at least one of oxides, carbides,nitrides and carbonitrides of at least one selected from the groupconsisting of metals of Groups 4a, 5a and 6a of the Periodic Table, Al,Si and Zn, and (ii) a shell layer that coats the outer periphery of thecore material and is composed of a second hard sintered body or secondceramics that has a different composition from the first hard sinteredbody.

[0015] Alternatively, the composite construction of the presentinvention based on the above-mentioned third method includes (i) acontinuous core material composed of a first hard sintered body obtainedby bonding, with a binder metal composed of an iron family metal havingan oxygen content concentration of 50 to 1000 ppm, a hard particlecomposed of at least one of carbides, nitrides and carbonitrides of atleast one selected from the group consisting of metals of Groups 4a, 5aand 6a of the Periodic Table, Si, Zn and Sn, or a first ceramicsobtained by boding, with a sintering additive containing an iron familymetal having an oxygen content concentration of 50 to 1000 ppm, a firstceramic particle composed of at least one of oxides, carbides, nitrides,carbonitrides and borides of at least one selected from the groupconsisting of metals of Groups 4a, 5a and 6a of the Periodic Table, Al,Si and Zn, and (ii) a shell layer that coats the outer periphery of thecore material and is composed of a second hard sintered body or secondceramics that has a different composition from the first hard sinteredbody.

[0016] In either case, it is desirable that in other compositeconstructions of the present invention, the ratio of the residual freecarbon amount C_(in) in the core material to the residual free carbonamount C_(out) in the shell layer, C_(in)/C_(out), is 0.5 to 2, aspreviously described. It is also desirable that the porosity in the corematerial of these composite constructions is not more than A04.

[0017] A method of manufacturing a composite construction according tothe present invention includes the steps of: (a) forming a core materialmolding by mixing a mixture of a metal powder that is a metalcomposition constituting a first hard particle composed of at least oneof carbides, nitrides and carbonitrides of metals of Groups 4a, 5a and6a of the Periodic Table, a binder metal powder, and an organic binder,or a mixture of a metal powder that is a metal composition constitutinga first ceramic particle composed of at least one of carbides, nitridesand carbonitrides selected from the group consisting of metals of Groups4a, 5a and 6a of the Periodic Table, Al, Si and Zn, a sintering additivepowder, and an organic binder, and then molding the mixture in acontinuous shape; (b) forming a composite molding by forming a shelllayer molding having a different composition from the molding obtainedin the step (a), and then disposing the shell layer molding so as tocoat the outer periphery of the core material obtained in the step (a);and (c) sintering the composite molding such that the metal powder ofthe metal composition constituting the first hard particle or the firstceramic particle is made into ceramic and its volume is expanded.

[0018] Other method of manufacturing a composite construction accordingto the present invention includes the steps of: (a) forming a corematerial molding by mixing a mixture of at least one powder selectedfrom the group consisting of oxides of metals of Groups 4a, 5a and 6a ofthe Periodic Table, SiO₂, ZnO and SnO₂, a binder metal powder, and anorganic binder, or a mixture of at least one powder selected from thegroup consisting of oxides of metals of Groups 4a, 5a and 6a of thePeriodic Table, SiO₂, ZnO and SnO₂, a sintering additive powder, and anorganic binder, then molding the mixture in a continuous shape; (b)forming a composite molding by forming a shell layer molding having adifferent composition from the molding obtained in the step (a), anddisposing the shell layer molding so as to coat the outer periphery ofthe core material molding obtained in the step (a); and (c) sinteringthe composite molding. This method is characterized in that at least onepowder selected from the group consisting of oxides of metals of Groups4a, 5a and 6a of the Periodic Table, SiO₂, ZnO, and SnO₂ is subjected tocarbonization or nitriding before sintering or during the time ofsintering.

[0019] In the step (c) of the above other manufacturing method, a heattreatment is carried out at 1000 to 1500° C. for 0.5 to 5 hours invaccum or inactive atmosphere such that at least one powder selectedfrom the group consisting of oxides of metals of Groups 4a, 5a and 6a ofthe Periodic Table, SiO₂, ZnO and SnO₂ is subjected to carbonization ornitriding, followed by sintering at 1300 to 1900° C. for 0.5 to 5 hoursin vaccum or inactive atmosphere. Further in the step (c), at least onepowder selected from the group consisting of oxides of metals of Groups4a, 5a and 6a of the Periodic Table, SiO₂, ZnO and SnO₂ is carbonized byreacting with the residual of the organic binder used in the step (a).

[0020] Still other method of manufacturing a composite constructionaccording to the present invention includes the steps of: (a) forming acore material molding by mixing a mixture of at least one of carbidepowder, nitride powder and carbonitride powder selected from the groupconsisting of metals of Groups 4a, 5a and 6a of the Periodic Table, Si,Zn and Sn, an iron family metal oxide powder, and an organic binder, ora mixture of at least one powder selected from the group consisting ofoxides, carbides, nitrides and carbonitrides of at least one selectedfrom the group consisting of metals of Groups 4a, 5a and 6a of thePeriodic Table, Al, Si and Zn, a sintering additive powder containing aniron family metal oxide powder, and an organic binder, then molding themixture in a continuous shape; (b) forming a composite molding byforming a shell layer molding having a different composition from themolding obtained in the step (a), and disposing the shell layer moldingso as to coat the outer periphery of the core material molding obtainedin the step (a); and (c) sintering the composite molding. The ironfamily metal oxide powder is subjected to reduction before sintering orduring the time of sintering.

[0021] In both manufacturing methods, it is desirable to add a 30 to 70%by weight organic binder. In an alternative, the composite constructionobtained in the step (b) may be stretched by co-extrusion. In otheralternative, a plurality of the composite constructions stretched byco-extrusion may be bound and again subjected to co-extrusion, therebymanufacturing a composite construction of multi-filament structure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a schematic perspective view showing one example of acomposite construction according to the present invention; and

[0023] FIGS. 2(a), 2(b) and 2(c) are images showing the manufacturingsteps of a composite construction according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0024] First Preferred Embodiment of the Invention

[0025] A first preferred embodiment of the invention will be describedbased on FIG. 1. As shown in FIG. 1, a composite construction 1 has sucha structure that the outer periphery of a continuous core material 2 iscoated with a shell layer 3.

[0026] As the material of a first hard sintered body constituting thecore material 2, there is for example a hard particle composed of one ormore of carbides, nitrides and carbonitrides of metals of Groups 4a, 5aand 6a of the Periodic Table, particularly at least one hard particleselected from the group consisting of WC, TiC, TiCN, TiN, TaC, NbC, ZrC,ZrN, VC, Cr₃C₂ and Mo₂C, more preferably a hard particle containing WC,TiC or TiCN, as a main component. The first hard sintered body isobtained by bonding these materials with a binder metal composed of atleast one selected from the group consisting of Fe, Co and Ni,particularly composed of Co and/or Ni. Particularly suitable first hardsintered body is a cemented carbide or cermet.

[0027] As the material of a first ceramics constituting the corematerial 2, besides the above-mentioned sintered body, there is forexample at least one of oxides, carbides, nitrides and carbonitridesselected from the group consisting of metals of Groups 4a, 5a and 6a ofthe Periodic Table, Al, Si and Zn, preferably at least one selected fromthe group consisting of Al₂O₃—TiC(TiCN), SiC, Si₃N₄, ZrO₂, TiB₂ andZnO—TiC, more preferably Al₂O₃—TiC(TiCN) and/or SiC. It is possible tocontain a suitable sintering additive composition into the firstceramics.

[0028] As the material of the shell layer 3 coating the outer peripheryof the core material 2, there is used a second hard sintered body orsecond ceramics that has a different composition from the core material2.

[0029] As the second hard sintered body or second ceramics, polycrystaldiamond, DLC (diamond like carbon), and cBN can also be used, besidesthe above-mentioned materials used for the core material 2.

[0030] As a suitable combination of core material 2 (i.e., the firsthard sintered body or first ceramics) and shell layer 3 (i.e., thesecond sintered body or second ceramics), there is for example oneselected from the group consisting of a cemented carbide and cermetcombination (referred to as “cemented carbide-cermet”), cementedcarbide-cBN, cemented carbide-diamond sintered body, cementedcarbide-alumina, cemented carbide silicon nitride, cermet-cementedcarbide, cermet-diamond sintered body, cermet-alumina, cermet-siliconnitride, (alumina, titanium carbonitride)-alumina, silicon carbidesilicon nitride, (silicon carbide, silicon nitride)-silicon nitride, andsilicon carbide-diamond sintered body. Among these, one selected fromthe group consisting of cemented carbide-cermet, cementedcarbide-diamond sintered body, and (alumina, titaniumcarbonitride)-alumina is most suitable in the point that it has a goodbalance of hardness and toughness and suitably used as a cutting tool.

[0031] The ratio of the residual free carbon amount C_(in) in the corematerial 2 to the residual free carbon amount C_(out) in the shell layer3, C_(in)/C_(out), is set to the range of 0.5 to 2. This prevents thatthe organic binder cannot completely be dissolved and volatized in thecore material 2 located at the inside of the composite construction 1,and a large amount of residual free carbon remain and the core material2 suffers from poor sintering. It is therefore possible to improve thestrength of the composite construction 1. That is, when the ratioC_(in)/C_(out) is smaller than 0.5, it is impossible to manufacture auniformly continuous composite construction 1. On the other hand, whenthe ratio C_(in)/C_(out) is over 2, the core material 2 suffers frompoor sintering, which lowers the strength of the composite construction1.

[0032] In order to densify the core material 2 and improve the strengthof the composite construction 1, the residual free carbon amount C_(in)in the core material 2 is not more than 1% by weight, preferably notmore than 0.5% by weight, more preferably not more than 0.2% by weight.In other words, the porosity based on ANSI/ASTM B276-54 (ISO 4505Cemented carbides-Metallographic determination of porosity anduncombined carbon) of the core material 2 and shell layer 3 in thecomposite construction 1 is respectively not more than A04 or B04,preferably not more than A02. The term “residual free carbon amount”used in the present invention indicates the ratio of the content of freecarbon composition, except for the carbon composition that constitutescarbide or carbonitride by bonding with metal, to the total amount ofthe core material 2 (or shell layer 3).

[0033] In order to improve the thermal conductivity of the compositeconstruction 1 and/or impart conductivity, it is desirable that the samemetal as the metal composition constituting the first hard particle orfirst ceramic particle is present in the core material 2, preferablypresent as a metal particle. Further, the same metal particle as themetal composition constituting the first hard particle or first ceramicparticle, or other metal particle can be dispersed and contained in theshell layer 3.

[0034] In order to improve the hardness and strength of the compositeconstruction 1 and also optimize the content of a binder material(binder metal or sintering additive) in the core material 2 and shelllayer 3, the average particle diameter of the first hard particle orfirst ceramic particle that constitutes the core material 2 ispreferably 0.05 to 10 μm, particularly 0.1 to 3 μm. On the other hand,in order to improve the toughness of the composite construction 1, theaverage particle diameter of the second hard particle or second ceramicparticle that constitutes the shell layer 3 is preferably 0.01 to 5 μm,particularly 0.01 to 2 μm.

[0035] To accomplish hardness and toughness compatibility in thecomposite construction 1, diameter D₁ of the core material 2 is 2 to1000 μm, preferably 10 to 500 μm, more preferably 50 to 200 μm, andthickness D₂ of the shell layer 3 is 1 to 50 μm, preferably 2 to 100 μm,more preferably 10 to 50 μm.

[0036] Further, according to the present invention, with theabove-mentioned configuration, the tensile stress present in theinterface between the core material 2 and shell layer 3 can be loweredto not more than 200 MPa, particularly 153 MPa, thereby preventingdelamination therebetween and deterioration of strength.

[0037] Furthermore, according to the present invention, a plurality ofthe composite constructions 1 in which the outer periphery of the corematerial 2 is coated with the shell layer 3 can be bound to obtain amulti-filament structure, as shown in FIG. 1, which further improves thetoughness of the composite construction. Even when binding a pluralityof the composite constructions 1, according to the present invention,the residual free carbon amount of the composite construction located inthe vicinity of the center of the bundle can be well reduced withoutlowing the binder burnout characteristic of an organic binder, thusleading to a high-strength construction that is densified as a whole.

[0038] According to the present invention, when the diameter orthickness of the composite construction 1 or its bundle is 1 mm or more,particularly 5 mm or more, further 10 mm or more, and/or the continuouslength is 10 mm or more, particularly 30 mm or more, further 50 mm ormore, it is possible to efficiently reduce the residual free carbonamount of the core material of the composite construction located in thevicinity of the center of the construction, and also eliminatedelamination between the core material 2 and shell layer 3.

[0039] Further in the present invention, a plurality of theabove-mentioned continuous composite constructions can be arranged inparallel so as to obtain a sheet. Further, a plurality of such sheetscan be laminated so that the adjacent continuous bodies of these sheetshave a predetermined angle, such as 0°, 45°, or 90°.

[0040] <Manufacturing Method>

[0041] A method of manufacturing a composite construction according tothe present invention will be described based on schematic images inFIGS. 2(a), 2(b) and 2(c).

[0042] First, there is mixed (i) 0 to 80% by weight, preferably 20 to70% by weight of a first hard particle that has an average particlediameter of 0.01 to 10 μm and is composed of one or more of carbides,nitrides and carbonitrides of metals of Groups 4a, 5a and 6a of thePeriodic Table, or a first ceramic particle composed of at least one ofoxides, carbides, nitrides and carbonitrides selected from the groupconsisting of metals of Groups 4a, 5a and 6a of the Periodic Table, Al,Si and Zn; and (ii) 3 to 80% by weight, preferably 5 to 50% by weight,more preferably 10 to 30% by weight of the same metal powder as a metalcomposition constituting the first hard particle or first ceramicparticle having an average particle diameter of 0.01 to 10 μm, and, ifrequired, 5 to 20% by weight of iron family metal powder having anaverage particle diameter of 0.01 to 10 μm, or 1 to 20% by weight of asintering additive composition powder. Subsequently, an organic bindersuch as paraffin wax, polystyrene, polyethylene, ethylene-ethylacrylate, ethylene-vinyl acetate, polybutyl methacrylate, polyethyleneglycol or dibutyl phthalate, a plasticizer and a solvent were added tothe mixture and then kneaded. This kneaded mixture is then formed into acylindrical shape by a molding method such as pressing or casting,thereby obtaining a core material molding 12 (see FIG. 2(a)).

[0043] Here, in order to obtain a uniform composite molding byco-extrusion to be described later, the content of the above organicbinder is 30 to 70% by volume, preferably 40 to 60% by volume.

[0044] On the other hand, a mixture constituting the shell layer 3having a different composition from the above-mentioned core materialmolding 12 is kneaded together with the above-mentioned binder. By amolding method such as pressing, extrusion or casting, this kneadedmixture is made into two shell layer moldings 13 having a half-cutcylindrical shape. These shell layer moldings 13 are disposed so as tocoat the outer periphery of the core material molding 12, therebyobtaining a molding 11 (see FIG. 2(a)).

[0045] Subsequently, the molding 11 is extruded (that is, the coremolding 12 and shell layer moldings 13 are co-extruded). This produces acomposite molding 15 stretched to a small diameter, in which the shelllayer moldings 13 surrounds the core material molding 12 (see FIG.2(b)). A construction of multi-filament structure is obtainable bybinding a plurality of the extruded continuous composite moldings 15 andperforming co-extrusion again (see FIG. 2(c)).

[0046] Further, if required, this stretched continuous composite molding15 can be co-extruded again so as to obtain a continuous shape having acircular, triangular or rectangular cross-section. In an alternative,the continuous composite moldings 15 are aligned to obtain a sheet, anda plurality of such sheets are prepared. These sheets are made into alaminated body in which the continuous composite moldings 15 arelaminated such that they are arranged in parallel, intersectperpendicularly, or have a predetermined angle, e.g., 45°. In otheralternative, the continuous composite molding 15 can be formed in anarbitrary shape, such as in a sheet, by a known molding method such asrapid prototyping method. In still other alternative, a sheet obtainedby aligning the composite moldings 15 as described above, or a compositeconstruction sheet obtained by slicing the former sheet in across-sectional direction can be laminated on or bonded to the surfaceof a conventional sintered body (bulk body) of cemented carbide.

[0047] The obtained composite molding 15 is subjected to binder burnouttreatment in which the temperature is heated to or maintained at 300 to700° C. for 10 to 200 hours, followed by sintering in vaccum or inactiveatmosphere at predetermined temperature and time, thereby obtaining acomposite construction of the present invention.

[0048] According to the present invention, carbide is formed by thereaction of the same metal powder as the metal composition of the firsthard particle or first ceramic particle added in the core material 2,with the residual free carbon remaining as a residue of the organicbinder during the time of sintering. This enables to be oxidized excessresidual free carbon. This also suppresses shrinkage accompanied bysintering to the core material, so that the residual stress between thecore material and shell layer is reduced and delamination therebetweenis prevented.

[0049] In the present invention, it is desirable that the temperatureheating rate in the range of 800° C. or higher is controlled at or below3° C./min because it is necessary to form carbide by allowing the metalpowder in the raw material to react with the residual free carbon afterbinder burnout treatment. It is also desirable to control thetemperature cooling rate at or below 3° C./min, in order to decrease theresidual stress between the core material 2 and shell layer 3.

[0050] In addition, according to the present invention, the volume ofpart of metal powder can be expanded by oxidation, boriding, ornitriding.

[0051] Second Preferred Embodiment of the Invention

[0052] A second preferred embodiment will be described based on FIG. 1.In this preferred embodiment, as the material constituting a corematerial 2, there is used, for example, a first hard particle composedof one or more of carbides, nitrides and carbonitrides of metals ofGroups 4a, 5a and 6a of the Periodic Table, Si, Zn and Sn, particularlyat least one selected from the group consisting of WC, TiC, TiCN, TiN,TaC, NbC, ZrC, ZrN, VC, Cr₃C₂ and Mo₂C, more preferably a first hardparticle containing WC, TiC or TiCN as a main component, and a firsthard sintered body, particularly cemented carbide or cermet, which isobtained by boding with a binder metal composed of at least one selectedfrom the group consisting of Fe, Co and Ni, particularly Co and/or Ni.

[0053] In addition, as the material constituting the core material 2, afirst ceramic particle similar to that in the foregoing preferredembodiment can be used suitably. It is possible to contain a suitablesintering additive composition into the first ceramics.

[0054] As the material of the shell layer 3 coating the outer peripheryof the core material 2, there is used a second hard sintered body orsecond ceramics having a different composition from the core material 2.

[0055] As the second hard sintered body or second ceramics, it ispossible to use polycrystal diamond, DLC (diamond like carbon) and cBN,besides the above-mentioned materials used for the core material 2.

[0056] Particularly suitable combination of core material 2 (i.e., thefirst hard sintered body or first ceramics) and shell layer 3 (i.e., thesecond sintered body or second ceramics) is for example one selectedfrom the group consisting of a cemented carbide and cermet combination(referred to as “cemented carbide-cermet”), cemented carbide-cBN,cemented carbide-diamond sintered body, cemented carbide-alumina,cemented carbide silicon nitride, cermet-cemented carbide,cermet-diamond sintered body, cermet-alumina, cermet-silicon nitride,(alumina, titanium carbonitride)-alumina, silicon carbide siliconnitride, (silicon carbide, silicon nitride) silicon nitride, siliconcarbide-diamond sintered body, alumina cermet, alumina-cemented carbide,(alumina, titanium carbonitride)-cemented carbide, (alumina, titaniumcarbonitride)-cermet, alumina-zirconia, (alumina, titaniumcarbonitride)-zirconia, (alumina, titanium carbonitride) (alumina,zirconia), silicon nitride-alumina, silicon nitride-(rare earth oxide,alumina, silica), diamond sintered body cBN, silicon nitride-cementedcarbide, silicon nitride-cermet, diamond-(alumina, titaniumcarbonitride), cBN-(alumina, titanium carbonitride), (alumina, titaniumcarbonitride) silicon carbide, and alumina-silicon carbide. Among these,one selected from the group consisting of cemented carbide cermet,cemented carbide-diamond sintered body, and (alumina, titaniumcarbonitride)-alumina is most suitable in the point that it has a goodbalance of hardness and toughness and suitably used as a cutting tool.

[0057] Here, the first hard particle or first ceramic particleconstituting the core material 2 is obtained by subjecting at least partof an oxide powder to carbonization and/or nitriding during the time ofsintering or before sintering. This prevents that the organic bindercannot completely be dissolved and volatized in the core material 2located at the inside of the composite construction 1, as the result, alarge amount of residual free carbon remain and the core material 2 ispoor sintering. It is therefore possible to improve the strength of thecomposite construction 1. It is desirable that the ratio of the residualfree carbon amount C_(in) in the core material 2 to the residual freecarbon amount C_(out) in the shell layer 3, C_(in)/C_(out), is 0.5 to 2.

[0058] In order to densify the core material 2 and improve the strengthof the composite construction 1, the residual free carbon amount C_(in)in the core material 2 is not more than 1% by weight, preferably notmore than 0.5% by weight, more preferably not more than 0.2% by weight.In other words, the porosity based on ANSI/ASTM B276-54 (ISO 4505Cemented carbides-Metallographic determination of porosity anduncombined carbon) of the core material 2 and shell layer 3 in thecomposite construction 1 is respectively not more than A04 or B04,preferably not more than A02.

[0059] In order that carbide, nitride, or carbonitride formed byreaction with a metal oxide of the composite construction 1 contributesto a particle-dispersion strengthened mechanism and improves thetoughness of the construction, the core material 2 may contain an oxideof the same metal as the metal composition constituting the first hardparticle or first ceramic particle. The shell layer 3 may contain thesame metal oxide particle as the metal composition constituting thefirst hard particle or first ceramic particle, or other metal oxideparticle.

[0060] The average particle diameter of the first hard particle or firstceramic particle constituting the core material 2, and the averageparticle diameter of the second hard particle or second ceramic particleconstituting the shell layer 3 may be in the same range as in theforegoing preferred embodiment. Diameter D₁ of the core material 2 andthickness D₂ of the shell layer 3 may be in the same range as in theforegoing preferred embodiment.

[0061] Third Preferred Embodiment of the Invention

[0062] A third preferred embodiment will be described based on FIG. 1.In this preferred embodiment, as the material constituting a corematerial 2, there is used, for example, a first hard particle composedof one or more of carbides, nitrides and carbonitrides of metals ofGroups 4a, 5a and 6a of the Periodic Table, Si, Zn and Sn, particularlyat least one selected from the group consisting of WC, TiC, TiCN, TiN,TaC, NbC, ZrC, ZrN, VC, Cr₃C₂ and Mo₂C, more preferably a first hardparticle containing WC, TiC or TiCN as a main component, and a firsthard sintered body, particularly cemented carbide or cermet, which isobtained by boding with a binder metal composed of at least one selectedfrom the group consisting of Fe, Co and Ni, particularly Co and/or Ni.

[0063] In addition, as the material constituting the core material 2, afirst ceramic particle similar to that in the foregoing preferredembodiment can be used suitably. It is possible to contain suitably asintering additive composition into the first ceramics.

[0064] As the material of the shell layer 3 coating the outer peripheryof the core material 2, there is used a second hard sintered body orsecond ceramics having a different composition from the core material 2.

[0065] As the second hard sintered body or second ceramics, it ispossible to use polycrystal diamond, DLC (diamond like carbon), and cBN,besides the above-mentioned materials used for the core material 2.

[0066] Particularly suitable combination of core material 2 (i.e., thefirst hard sintered body or first ceramics) and shell layer 3 (i.e., thesecond sintered body or second ceramics) is for example one selectedfrom the group consisting of a cemented carbide and cermet combination(referred to as “cemented carbide-cermet”), cemented carbide-cBN,cemented carbide-diamond sintered body, cemented carbide-alumina,cemented carbide silicon nitride, cermet-cemented carbide,cermet-diamond sintered body, cermet-alumina, cermet-silicon nitride,(alumina, titanium carbonitride)-alumina, silicon carbide siliconnitride, (silicon carbide, silicon nitride)-silicon nitride, siliconcarbide-diamond sintered body, alumina cermet, alumina-cemented carbide,(alumina, titanium carbonitride)-cemented carbide, (alumina, titaniumcarbonitride)-cermet, alumina-zirconia, (alumina, titaniumcarbonitride)-zirconia, (alumina, titanium carbonitride) (alumina,zirconia), silicon nitride-alumina, silicon nitride-(rare earth oxide,alumina, silica), diamond sintered body cBN, silicon nitride-cementedcarbide, silicon nitride-cermet, diamond-(alumina, titaniumcarbonitride), cBN-(alumina, titanium carbonitride), (alumina, titaniumcarbonitride)-silicon carbide, and alumina-silicon carbide. Among these,one selected from the group consisting of cemented carbide cermet,cemented carbide-diamond sintered body, and (alumina, titaniumcarbonitride)-alumina is most suitable in the point that it has a goodbalance of hardness and toughness and suitably used as a cutting tool.

[0067] Here, the first hard particle or first ceramic particleconstituting the core material 2 is obtained by adding an oxide powderof iron family metal constituting a binder phase or sintering additiveand subjecting at least part of the oxide powder to reduction during thetime of sintering or before sintering. This prevents that the organicbinder cannot completely be dissolved and volatized in the core material2 located at the inside of the composite construction 1, as the result,a large amount of residual free carbon remain and the core material 2suffers from sintering. It is therefore possible to improve the strengthof the composite construction 1. It is desirable that the ratio of theresidual free carbon amount C_(in) in the core material 2 to theresidual free carbon amount C_(out) in the shell layer 3,C_(in)/C_(out), is 0.5 to 2.

[0068] In order to densify the core material 2 and improve the strengthof the composite construction 1, the residual free carbon amount C_(in)in the core material 2 is not more than 1% by weight, preferably notmore than 0.5% by weight, more preferably not more than 0.2% by weight.In other words, the porosity based on ANSI/ASTM B276-54 (ISO 4505Cemented carbides-Metallographic determination of porosity anduncombined carbon) of the core material 2 and shell layer 3 in thecomposite construction 1 is respectively not more than A04 or B04,preferably not more than A02.

[0069] In order that carbide, nitride, or carbonitride formed byreaction with a metal oxide of the composite construction 1 contributesto a particle-dispersion strengthened mechanism and improves thetoughness of the construction, the core material 2 may contain an oxideof the same metal as the metal composition constituting the first hardparticle or first ceramic particle. The shell layer 3 may contain thesame metal oxide particle as the metal composition constituting thefirst hard particle or first ceramic particle, or other metal oxideparticle.

[0070] The average particle diameter of the first hard particle or firstceramic particle constituting the core material 2, and the averageparticle diameter of the second hard particle or second ceramic particleconstituting the shell layer 3 may be in the same range as in theforegoing preferred embodiment. Diameter D₁ of the core material 2 andthickness D₂ of the shell layer 3 may be in the same range as in theforegoing preferred embodiment.

[0071] <Manufacturing Method>

[0072] A method of manufacturing a composite construction according tothe foregoing preferred embodiment will be described based on theschematic images in FIGS. 2(a), 2(b) and 2(c).

[0073] First, there is mixed (i) 0.01 to 50% by weight, preferably 0.1to 20% by weight, more preferably 10 to 20% by weight of an oxide powderthat has an average particle diameter of 0.01 to 10 μm and is composedof one selected from metals of Groups 4a, 5a and 6a of the PeriodicTable, Si, Zn and Sn; and 30 to 80% by weight, preferably 50 to 70% byweight of a first hard particle that has an average particle diameter of0.01 to 10 μm and is composed of one or more of carbides, nitrides andcarbonitrides of metals Groups 4a, 5a and 6a of the Periodic Table, Si,Zn and Sn, or a first ceramic powder composed of at least one of oxides,carbides, nitrides and carbonitrides selected from the group consistingof metals of Groups 4a, 5a and 6a of the Periodic Table, Al, Si and Zn;and, if required, 30% or less, preferably 20% by weight or less of thesame metal powder as the metal composition constituting the first hardparticle or first ceramic particle, and, if required, 5 to 20% by weightof iron family metal powder having an average particle diameter of 0.01to 10 μm, and 1 to 20% by weight of a sintering additive compositionpowder. Subsequently, an organic binder such as paraffin wax,polystyrene, polyethylene, ethylene-ethyl acrylate, ethylene-vinylacetate, polybutyl methacrylate, polyethylene glycol or dibutylphthalate, a plasticizer and a solvent are added to the mixture and thenkneaded. This kneaded mixture is then formed into a cylindrical shape bya molding method such as pressing or casting, thereby obtaining a corematerial molding 12 (see FIG. 2(a)).

[0074] The same subsequent steps as in the foregoing preferredembodiment are performed to obtain a composite construction 15. Thiscomposite construction 15 is subjected to binder burnout treatment inwhich the temperature is heated to or maintained at 100 to 700° C. for10 to 200 hours, followed by sintering in vaccum or inactive atmosphereat predetermined temperature and time, thereby obtaining a compositeconstruction of the present invention.

[0075] According to the present invention, the same metal oxide powderas the metal composition of the first hard particle or first ceramicparticle added in the core material 2 is subjected to carbonization ornitriding during the time of sintering, such that oxygen is releasedand, in particular, allowed to react with the residual free carbonremaining as a residue of the organic binder, thereby forming carbide.This enables to be oxidized excess residual free carbon. In addition,the metal oxide powder is changed to at least one selected from thegroup consisting of carbide, nitride and carbonitride that have highhardness and strength, thus leading to a sintered body excellent inhardness, toughness and strength.

[0076] In the case of adding an iron family metal oxide powder, the ironfamily metal oxide is reduced to an iron family metal. In thisreduction, oxygen is released and, in particular, allowed to react withthe residual free carbon remaining as a residue of the organic binder,thereby forming carbide. This enables to be oxidized excess residualfree carbon. In addition, the iron family metal acts as a binder phaseor sintering additive thus leading to a sintered body excellent inhardness, toughness and strength.

[0077] It is also possible to control the oxygen content concentrationin the binder phase or intergranular phase (sintering additive phase),depending on the amount of the iron family metal oxide powder andmanufacturing conditions.

[0078] Because it is necessary to form carbide by allowing the metalpowder in the raw material to react with the residual free carbongenerated by binder burnout treatment, it is desirable to perform a heattreatment in vaccum or inactive gas atmosphere at 1000 to 1500° C.,particularly 1150 to 1400° C., for 0.5 to 5 hours, particularly 1 to 3hours. It is also desirable that the temperature heating rate in therange of 800° C. or higher is controlled at or below 3° C./min. It isdesirable to carry out sintering in vaccum or inactive atmosphere at1300 to 1900° C., particularly 1400 to 1800° C., for 0.5 to 5 hours,particularly 1 to 5 hours. It is also desirable to control thetemperature cooling rate at or below 3° C./min, in order to decrease theresidual stress between the core material 2 and shell layer 3.

[0079] In addition, according to the present invention, it is possiblethat a metal powder is added together with an oxide, and the volume ofthe metal powder is partly expanded by oxidation, boriding, ornitriding. Otherwise, this preferred embodiment is the same as theforegoing preferred embodiment, and therefore, its description isomitted.

EXAMPLES Example 1

[0080] To a mixture of 75% by weight of WC powder having an averageparticle diameter of 1.5 μm, 10% by weight of Co powder having anaverage particle diameter of 1 μm, 5% by weight of TiC powder having anaverage particle diameter of 2 μm, and 10% by weight of metal W powderhaving an average particle diameter of 1 μm, cellulose and polystyreneglycol as organic binder, and polyvinyl alcohol as solvent were added inthe total amount of 100 parts by volume. This mixture was then kneadedand extruded in a cylindrical shape, thereby obtaining a core materialmolding.

[0081] On the other hand, to a mixture of 50% by weight of TiCN powderhaving an average particle diameter of 1.5 μm, 10% by weight of TiCpowder having an average particle diameter of 1.5 μm, 7% by weight of Copowder having an, average particle diameter of 1 μm, 20% by weight of WCpowder having an average particle diameter of 1.5 μm, 7% by weight ofMo₂C powder having an average particle diameter of 2 μm, and 6% byweight of VC powder having an average particle diameter of 2 μm, thesame organic binders and solvent as mentioned above were added. Thismixture was then kneaded and extruded to obtain two shell layer moldingshaving a half-cut cylindrical shape. The two shell layer moldings weredisposed so as to coat the outer periphery of the core material molding,thereby obtaining a molding.

[0082] Subsequently, this molding was co-extruded to obtain a stretchedcomposite construction, and 100 pieces of the stretched compositeconstructions were bound and co-extruded again, thereby obtaining acomposite molding of multi-filament type.

[0083] Then, this multi-filament type composite molding was cut off into100 mm length and aligned in parallel to obtain a sheet. These sixsheets were laminated such that the composite constructions in theadjacent sheets have an angle of 45°, thereby obtaining a rectangularparallelepiped laminated molding.

[0084] Thereafter, this laminated molding was subjected to binderburnout treatment by raising the temperature from 300 to 700° C. in 100hours. Subsequently, the temperature was raised at a temperature heatingrate of 2.5° C./min, sintering was performed in vaccum at 1450° C. for 2hours, and the temperature was then cooled at 3° C./min, therebyobtaining a composite construction.

[0085] In this composite construction, the residual free carbon amountC_(in) in the core material and the residual free carbon amount C_(out)in the shell layer were respectively measured based on JISH1402. As theresult, the former was 0.3% by weight, the latter was 0.26% by weight,and the ratio C_(in)/C_(out) was 1.2.

[0086] The cross-section of the composite construction was observed. Thediameter of the core material was 90 μm and the thickness of the shelllayer was 5 μm. Between the core material and shell layer, nodelamination was observed. The residual stress in the interface betweenthe core material and shell layer was measured by X-ray diffraction andit was found that tensile stress of 31 MPa was present. The three-pointbending strength based on JISR1601 of the composite construction was2000 MPa. The porosity based on ANSI/ASTM B276-54 (ISO 4505 Cementedcarbides-Metallographic determination of porosity and uncombined carbon)of the shell layer was A00, and that of the core material was A01.

Comparative Example 1

[0087] A composite construction was manufactured in the same manner asExample 1, except that the material for core material was changed to amixture of 85% by weight of WC powder having an average particlediameter of 1.5 μm, 10% by weight of Co powder having an averageparticle diameter of 1 μm, and 5% by weight of TiC powder having anaverage particle diameter of 2 μm. The same evaluation was conducted andthe following results were obtained. The residual free carbon amountC_(in) in the core material was 3.06% by weight, the residual freecarbon amount C_(out) in the shell layer was 0.62% by weight, and theratio C_(in)/C_(out) was 4.9. In the cross-section of the compositeconstruction was observed, a large number of delaminations were observedin the interface between the core material and shell layer. By measuringthe residual stress in the interface between the core material and shelllayer, it was found that tensile stress of 255 MPa was present. Thethree-point bending strength of the composite construction was 500 MPa.The porosity of the shell layer was C01, and that of the core materialwas C06.

Example 2

[0088] A composite construction was manufactured in the same manner asExample 1, except that the material for shell layer in Example 1 waschanged to a mixture of 80% by weight of WC powder having an averageparticle diameter of 0.2 μm, 8% by weight of Co powder having an averageparticle diameter of 0.5 μm, 0.3% by weight of VC powder having anaverage particle diameter of 0.8 μm, 0.7% by weight of Cr₃C₂ powderhaving an average particle diameter of 0.8 μm, and 11% by weight ofmetal W powder having an average particle diameter of 0.3 μm. The sameevaluation was conducted and the following results were obtained. Theresidual free carbon amount C_(in) in the core material was 0.38% byweight, the residual free carbon amount C_(out) in the shell layer was0.30% by weight, and the ratio C_(in)/C_(out) was 1.3. By measuring theresidual stress in the interface between the core material and shelllayer by X-ray diffraction, it was found that tensile stress of 43 MPawas present. The three-point bending strength of the compositeconstruction was 1800 MPa. The porosity of the shell layer was A01, andthat of the core material was A02.

Example 3

[0089] A composite construction was manufactured in the same manner asExample 1, except that (i) the material for core material in Example 1was changed to a mixture of 50% by weight of silicon carbide powderhaving an average particle diameter of 2 μm, 23% by weight of aluminumnitride powder having an average particle diameter of 2 μm, 17% byweight of alumina powder, and 10% by weight of metal silicon powder,(ii) the material for shell layer in Example 1 was changed to a mixtureof 97% by weight of Si₃N₄ powder having an average particle diameter of2 μm, 2% by weight of Y₂O₃ powder having an average particle diameter of1.5 μm, and 1% by weight of Al₂O₃ powder having an average particlediameter of 1 μm, and (iii) the temperature at which the constructionwas sintered was changed to 1900° C. The same evaluation was conductedand the following results were obtained. The residual free carbon amountC_(in) in the core material was 0.20% by weight, the residual freecarbon amount C_(out) in the shell layer was 0.21% by weight, and theratio C_(in)/C_(out) was 0.95. By measuring the residual stress in theinterface between the core material and shell layer, it was found thattensile stress of 104 MPa was present. The three-point bending strengthof the composite construction was 950 MPa. The porosity of the shelllayer was A01, and that of the core material was A01.

Example 4

[0090] To a mixture of 80% by weight of WC powder having an averageparticle diameter of 1.5 μm, 10% by weight of Co powder having anaverage particle diameter of 1 μm, 5% by weight of TiC powder having anaverage particle diameter of 2 μm, and 5% by weight of TiO₂ powderhaving an average particle diameter of 1 μm, cellulose and polystyreneglycol as organic binder, and polyvinyl alcohol as solvent were added inthe total amount of 100 parts by volume. This mixture was then kneadedand extruded in a cylindrical shape, thereby obtaining a core materialmolding.

[0091] On the other hand, to a mixture of 50% by weight of TiCN powderhaving an average particle diameter of 1.5 μm, 13% by weight of TiCpowder having an average particle diameter of 1.5 μm, 7% by weight of Copowder having an average particle diameter of 1 μm, and 19% by weight ofWC powder having an average particle diameter of 1.5 μm, 6% by weight ofMO₂C powder having an average particle diameter of 2 μm, and 5% byweight of VC powder having an average particle diameter of 2 μm, thesame organic binders and solvent as mentioned above were added. Thismixture was then kneaded and extruded to obtain two shell layer moldingshaving a half-cut cylindrical shape. The two shell layer moldings weredisposed so as to coat the outer periphery of the core material molding,thereby obtaining a molding.

[0092] Subsequently, this molding was co-extruded to obtain a stretchedcomposite construction, and 100 pieces of the stretched compositeconstructions were bound and co-extruded again, thereby obtaining acomposite molding of multi-filament type.

[0093] Then, this multi-filament type composite molding was cut off into100 mm length and aligned in parallel to obtain a sheet. These sixsheets were laminated such that the composite constructions in theadjacent sheets have an angle of 45°, thereby obtaining a rectangularparallelepiped laminated molding.

[0094] Thereafter, this laminated molding was subjected to binderburnout treatment by raising the temperature from 100 to 700° C. in 100hours. Subsequently, the temperature was raised at a temperature heatingrate of 2.5° C./min, and maintained at 1300° C. for 1 hour in vaccum,followed by sintering at 1450° C. for 2 hours. Thereafter, thetemperature was cooled at 3° C./min, thereby obtaining a compositeconstruction.

[0095] Free carbon amount in the obtained composite construction as awhole was measured. The residual free carbon amount C_(in) in the corematerial and the residual free carbon amount C_(out) in the shell layerwere measured, and the former was 0.01% by weight and the latter was0.1% by weight.

[0096] The cross-section of the composite construction was observed. Thediameter of the core material was 90 μm and the thickness of the shelllayer was 5 μm. No delamination was observed between the core materialand shell layer. The residual stress in the interface between the corematerial and shell layer was measured by X-ray diffraction, and it wasfound that compressive stress of 230 MPa was present in the corematerial 2. The three-point bending strength of the compositeconstruction was 2500 MPa. The porosity of the shell layer was A02, andthat of the core material was A01.

Comparative Example 2

[0097] A composite construction was manufactured in the same manner asExample 4, except that the material for core material in Example 1 waschanged to a mixture of 85% by weight of WC powder having an averageparticle diameter of 1.5 μm, 10% by weight of Co powder having anaverage particle diameter of 1 μm, and 5% by weight of TiC powder havingan average particle diameter of 2 μm. The same evaluation was conductedand the following results were obtained. The residual free carbon amountC_(in) in the core material was 4.56% by weight, and the residual freecarbon amount C_(out) in the shell layer was 2.00% by weight. In thecross-section of the composite construction, a large number ofdelaminations were observed in the interface between the core materialand shell layer. The three-point bending strength of the compositeconstruction was 500 MPa. The porosity of the shell layer was C01, andthat of the core material was C06.

Example 5

[0098] A composite construction was manufactured in the same manner asExample 1, except that the material for shell layer in Example 4 waschanged to a mixture of 50% by weight of TiCN powder having an averageparticle diameter of 1.5 μm, 10% by weight of TiC powder having anaverage particle diameter of 1.5 μm, 7% by weight of Co powder having anaverage particle diameter of lam, 19% by weight of WC powder having anaverage particle diameter of 1.5 μm, 6% by weight of MO₂C powder havingan average particle diameter of 2 μm, 5% by weight of VC powder havingan average particle diameter of 2 μm, and 3% by weight of TiO₂ powderhaving an average particle diameter of 1.0 μm. The same evaluation wasconducted and the following results were obtained.

[0099] The residual free carbon amount C_(in) in the core material was0.01% by weight, and the residual free carbon amount C_(out) in theshell layer was 0.01% by weight. The residual stress in the interfacebetween the core material and shell layer was measured by X-raydiffraction, and it was found that compressive stress of 200 MPa waspresent in the core material 2. The three-point bending strength of thecomposite construction was 2600 MPa. The porosity of the shell layer wasA00, and that of the core material was A00.

Example 6

[0100] A laminated molding having a rectangular parallelepiped shape wasmanufactured in the same manner as Example 1, except that (i) thematerial for core material in Example 4 was changed to a mixture of 70%by weight of Al₂O₃ powder having an average particle diameter of 0.2 μm,21% by weight of TiC powder having an average particle diameter of 0.5μm, 5% by weight of TiN powder having an average particle diameter of0.5 μm, 0.5% by weight of Y₂O₃ having an average particle diameter of 1μm, 0.5% by weight of MgO having an average particle diameter of lam,0.5% by weight of Co₃O₄ having an average particle diameter of 1 μm, and2.5% by weight of TiO₂ having an average particle diameter of 1.5 μm,and (ii) the material for shell layer in Example 4 was changed to amixture of 84% by weight of Al₂O₃ powder having an average particlediameter of 0.2 μm, 12% by weight of ZrO₂ powder having an averageparticle diameter of 0.5 μm, 0.5% by weight of Y₂O₃ having an averageparticle diameter of 1 μm, 0.5% by weight of MgO having an averageparticle diameter of 1 μm, 0.5% by weight of Co₃O₄ having an averageparticle diameter of 1 μm, and 2.5% by weight of TiO₂ powder having anaverage particle diameter of 1.5 μm.

[0101] Subsequently, this laminated molding was subjected to binderburnout treatment by raising the temperature from 100 to 700° C. in 100hours. Then, the temperature was raised at a temperature heating rate of2.5° C./min, and maintained at 1300° C. for 1 hour in vaccum, followedby sintering at 1600° C. for 2 hours. Thereafter, the temperature wascooled at 3° C./min, thereby obtaining a composite construction. Thesame evaluation as in Example 4 was conducted and the following resultswere obtained.

[0102] The residual free carbon amount C_(in) in the core material was0.015% by weight, and the residual free carbon amount C_(out) in theshell layer was 0.012% by weight. By measuring the residual stress inthe interface between the core material and shell layer, it was foundthat compressive stress of 250 MPa was present in the core material 2.The three-point bending strength of the composite construction was 950MPa. The porosity of the shell layer was A01, and that of the corematerial was A01.

Example 7

[0103] A laminated molding having a rectangular parallelepiped shape wasmanufactured in the same manner as Example 1, except that (i) thematerial for core material in Example 4 was changed to a mixture of 92%by weight of Si₃N₄ powder having an average particle diameter of 0.2 μm,6% by weight of Y₂O₃ powder having an average particle diameter of 0.5μm, 1.5% by weight of Al₂O₃ powder having an average particle diameterof 0.5 μm, and 0.5% by weight of Si powder having an average particlediameter of 1 μm, and (ii) the material for shell layer in Example 4 waschanged to a mixture of 90% by weight of SiC powder having an averageparticle diameter of 0.5 μm, 6% by weight of Al₂O₃ powder having anaverage particle diameter of 0.5 μm, 3.5% by weight of Y₂O₃ powderhaving an average particle diameter of 0.5 μm, and 0.5% by weight ofSiO₂ powder having an average particle diameter of 1 μm.

[0104] Subsequently, this laminated molding was subjected to binderburnout treatment by raising the temperature from 100 to 700° C. in 100hours. Then, the temperature was raised at a temperature heating rate of2.5° C./min, and maintained at 1300° C. for 1 hour in vaccum, followedby sintering at 1900° C. for 2 hours. Thereafter, the temperature wascooled at 3° C./min, thereby obtaining a composite construction. Thesame evaluation as in Example 4 was conducted and the following resultswere obtained.

[0105] The residual free carbon amount C_(in) in the core material was0.01% by weight, and the residual-free carbon amount C_(out) in theshell layer was 0.012% by weight. By measuring the residual stress inthe interface between the core material and shell layer, it was foundthat compressive stress of 200 MPa was present in the core material 2.The three-point bending strength of the composite construction was 950MPa. The porosity of the shell layer was A01, and that of the corematerial was A01.

Example 8

[0106] A laminated molding having a rectangular parallelepiped shape wasmanufactured in the same manner as Example 1, except that (i) thematerial for core material in Example 4 was changed to a mixture of 67%by weight of Al₂O₃ powder having an average particle diameter of 0.2 μm,21% by weight of TiC powder having an average particle diameter of 0.5μm, 5% by weight of TiN powder having an average particle diameter of0.5 μm, 0.5% by weight of Y₂O₃ powder having an average particlediameter of 1 μm, 0.5% by weight of MgO powder having an averageparticle diameter of 1 μm, 3.5% by weight of Co₃O₄ powder having anaverage particle diameter of 1 μm, and 2.5% by weight of TiO₂ powderhaving an average particle diameter of 1.5 μm, and (ii) the material forshell layer in Example 4 was changed to a mixture of 84% by weight ofAl₂O₃ powder having an average particle diameter of 0.2 μm, 12% byweight of ZrO₂ powder having an average particle diameter of 0.5 μm,0.5% by weight of Y₂O₃ powder having an average particle diameter of 1μm, 0.5% by weight of MgO powder having an average particle diameter of1 μm, 0.5% by weight of Co₃O₄ powder having an average particle diameterof 1 μm, and 2.5% by weight of TiO₂ powder having an average particlediameter of 1.5 μm.

[0107] Subsequently, this laminated molding was subjected to binderburnout treatment by raising the temperature from 100 to 700° C. in 100hours. Then, the temperature was raised at a temperature heating rate of2.5° C./min, and maintained at 1300° C. for 1 hour in vaccum, followedby sintering at 1600° C. for 2 hours. Thereafter, the temperature wascooled at 3° C./min, thereby obtaining a composite construction. Thesame evaluation as in Example 4 was conducted and the following resultswere obtained.

[0108] The residual free carbon amount C_(in) in the core material was0.016% by weight, and the residual free carbon amount C_(out) in theshell layer was 0.013% by weight. By measuring the residual stress inthe interface between the core material and shell layer, it was foundthat compressive stress of 260 MPa was present in the core material 2.The three-point bending strength of the composite construction was 930MPa. The porosity of the shell layer was A01, and that of the corematerial was A01. Further, the oxygen content in the intergranular phasepart was measured by energy dispersive spectroscopy (EDS) attached totransmission electron microscope (TEM), and its result was 90 ppm.

What is claimed is:
 1. A composite construction comprising a continuouscore material composed of a first hard sintered body or first ceramics,and a shell layer that coats the outer periphery of said core materialand is composed of a second hard sintered body or second ceramics havinga different composition from said first hard sintered body and firstceramics, wherein the ratio of the residual free carbon amount C_(in) inthe core material to the residual free carbon amount C_(out) in theshell layer, C_(in)/C_(out), is 0.5 to
 2. 2. The composite constructionaccording to claim 1 wherein said first hard sintered body is obtainedby bonding, with a binder metal, a first hard particle composed of atleast one selected from carbides, nitrides and carbonitrides of metalsof Groups 4a, 5a and 6a of the Periodic Table.
 3. The compositeconstruction according to claim 1 wherein said first ceramics isobtained by sintering, with a sintering additive, a first ceramicparticle composed of at least one of oxides, carbides, nitrides,carbonitrides and borides selected from the group consisting of metalsof Groups 4a, 5a and 6a of the Periodic Table, Al, Si and Zn.
 4. Thecomposite construction according to claim 1 wherein the residual freecarbon amount C_(in) in said core material is not more than 1% byweight.
 5. The composite construction according to claim 1 wherein thesame metal as a metal composition constituting said first hard particleor said first ceramic particle is present in said core material.
 6. Thecomposite construction according to claim 1 wherein tensile stress inthe surface of said core material is not more than 200 MPa.
 7. Thecomposite construction according to claim 1, which is obtained bybinding a plurality of said composite constructions.
 8. A compositeconstruction comprising a continuous core material composed of a firsthard sintered body or first ceramics, and a shell layer that coats theouter periphery of said core material and is composed of a second hardsintered body or second ceramics having a different composition fromsaid first hard sintered body and first ceramics, wherein the porosityof said core material and said shell layer is not more than A04, B04, orC02.
 9. The composite construction according to claim 8 wherein saidfirst hard sintered body is obtained by bonding, with a binder metal, afirst hard particle composed of at least one selected from carbides,nitrides and carbonitrides of metals of Groups 4a, 5a and 6a of thePeriodic Table.
 10. The composite construction according to claim 8wherein the residual free carbon amount C_(in) in said core material isnot more than 1% by weight.
 11. The composite construction according toclaim 8 wherein the same metal as a metal composition constituting saidfirst hard particle or said first ceramic particle is present in saidcore material.
 12. The composite construction according to claim 8wherein tensile stress in the surface of said core material is not morethan 200 MPa.
 13. The composite construction according to claim 8, whichis obtained by binding a plurality of said composite constructions. 14.A composite construction comprising: a continuous core material composedof a first hard sintered body obtained by bonding, with a binder metal,a first hard particle composed of at least one of carbides, nitrides andcarbonitrides that are obtained by performing carbonization and/ornitriding of at least one oxide selecting from the group consisting ofmetals of Groups 4a, 5a and 6a of the Periodic Table, Si, Zn and Sn, ora first ceramics obtained by bonding, with a sintering additive, a firstceramic particle composed of at least one of carbides, nitrides andcarbonitrides that are obtained by performing carbonization and/ornitriding of at least one oxide selected from the group consisting ofmetals of Groups 4a, 5a and 6a of the Periodic Table, Al, Si and Zn; anda shell layer that coats the outer periphery of said core material andis composed of a second hard sintered body or second ceramics having adifferent composition from said first hard sintered body.
 15. Thecomposite construction according to claim 14 wherein the ratio of theresidual free carbon amount C_(in) in the core material to the residualfree carbon amount C_(out) in the shell layer, C_(in)/C_(out), is 0.5 to2.
 16. The composite construction according to claim 14 wherein theporosity of said core material is not more than A04.
 17. The compositeconstruction according to claim 14, which is obtained by binding aplurality of said composite constructions.
 18. A composite constructioncomprising: a continuous core material composed of (i) a first hardsintered body obtained by bonding, with a binder metal, a hard particlein which at least one oxide selected from metals of Groups 4a, 5a and 6aof the Periodic Table, Si, Zn and Sn is mingled with at least one ofcarbides, nitrides and carbonitrides, or (ii) a first ceramics obtainedby bonding, with a sintering additive, a first ceramic particle in whichat least one oxide selected from the group consisting of metals ofGroups 4a, 5a and 6a of the Periodic Table, Al, Si and Zn is mingledwith at least one of carbides, nitrides, carbonitrides and borides; anda shell layer that coats the outer periphery of said core material andis composed of a second hard sintered body or second ceramics having adifferent composition from said first hard sintered body.
 19. Thecomposite construction according to claim 18 wherein the ratio of theresidual free carbon amount C_(in) in the core material to the residualfree carbon amount C_(out) in the shell layer, C_(in)/C_(out) is 0.5 to2.
 20. The composite construction according to claim 18 wherein theporosity of said core material is not more than A04.
 21. The compositeconstruction according to claim 18, which is obtained by binding aplurality of said composite constructions.
 22. A composite constructioncomprising: a continuous core material composed of (i) a first hardsintered body obtained by bonding, with a binder metal composed of aniron family metal obtained by reducing an oxide, a first hard particlecomposed of at least one of carbides, nitrides and carbonitrides of atleast one selected from metals of Groups 4a, 5a and 6a of the PeriodicTable, Si, Zn and Sn, or (ii) a first ceramics obtained by bonding, witha sintering additive containing an iron family metal obtained byreducing an oxide, a first ceramic particle composed of at least one ofoxides, carbides, nitrides and carbonitrides of at least one selectedfrom the group consisting of metals of Groups 4a, 5a and 6a of thePeriodic Table, Al, Si and Zn; and a shell layer that coats the outerperiphery of said core material and is composed of a second hardsintered body or second ceramics having a different composition fromsaid first hard sintered body.
 23. The composite construction accordingto claim 22 wherein the ratio of the residual free carbon amount C_(in)in the core material to the residual free carbon amount C_(out) in theshell layer, C_(in)/C_(out), is 0.5 to
 2. 24. The composite constructionaccording to claim 22 wherein the porosity of said core material is notmore than A04.
 25. The composite construction according to claim 22,which is obtained by binding a plurality of said compositeconstructions.
 26. A composite construction comprising: a continuouscore material composed of (i) a first hard sintered body obtained bybonding, with a binder metal composed of an iron family metal having anoxygen content concentration of 50 to 1000 ppm, a hard particle composedof at least one of carbides, nitrides and carbonitrides of at least oneselected from metals of Groups 4a, 5a and 6a of the Periodic Table, Si,Zn and Sn, or (ii) a first ceramics obtained by bonding, with asintering additive containing an iron family metal having an oxygencontent concentration of 50 to 1000 ppm, a first ceramic particlecomposed of at least one of oxides, carbides, nitrides, borides andcarbonitrides of at least one selected from the group consisting ofmetals of Groups 4a, 5a and 6a of the Periodic Table, Al, Si and Zn; anda shell layer that coats the outer periphery of said core material andis composed of a second hard sintered body or second ceramics having adifferent composition from said first hard sintered body.
 27. Thecomposite construction according to claim 26 wherein the ratio of theresidual free carbon amount C_(in) in the core material to the residualfree carbon amount C_(out) in the shell layer, C_(in)/C_(out) is 0.5 to2.
 28. The composite construction according to claim 26 wherein theporosity of said core material is not more than A04.
 29. The compositeconstruction according to claim 26, which is obtained by binding aplurality of said composite constructions.
 30. A method of manufacturinga composite construction comprising the steps of: (a) forming a corematerial molding by mixing a mixture of a metal powder that is a metalcomposition constituting a first hard particle composed of at least oneof carbides, nitrides and carbonitrides of metals of Groups 4a, 5a and6a of the Periodic Table, a binder metal powder, and an organic binder,or a mixture of a metal powder that is a metal composition constitutinga first ceramic particle composed of at least one of carbides, nitridesand carbonitrides selected from the group consisting of metals of Groups4a, 5a and 6a of the Periodic Table, Al, Si and Zn, a sintering additivepowder, and an organic binder, and then molding said mixture in acontinuous shape; (b) forming a composite molding by forming a shelllayer molding having a different composition from said molding obtainedin the step (a), and disposing said shell layer molding so as to coatthe outer periphery of said core material molding obtained in the step(a); and (c) sintering said composite molding such that said metalpowder of said metal composition constituting said first hard particleor said first ceramic particle is made into ceramic and its volume isexpanded.
 31. The method according to claim 30 wherein said organicbinder is added in an amount of 30 to 70% by volume.
 32. The methodaccording to claim 30 wherein said composite molding obtained in thestep (b) is stretched by co-extrusion.
 33. The method according to claim30 wherein a composite construction having a multi-filament structure ismanufactured by binding a plurality of said composite moldings stretchedby co-extrusion, and performing co-extrusion again.
 34. A method ofmanufacturing a composite construction comprising the steps of: (a)forming a core material molding by mixing a mixture of at least onepowder selected from the group consisting of oxides of metals of Groups4a, 5a and 6a of the Periodic Table, SiO₂, ZnO and SnO₂, a binder metalpowder, and an organic binder, or a mixture of at least one powderselected from the group consisting of oxides of metals of Groups 4a, 5aand 6a of the Periodic Table, SiO₂, ZnO and SnO₂, a sintering additivepowder, and an organic binder, and then molding said mixture in acontinuous shape; (b) forming a composite molding by forming a shelllayer molding having a different composition from said molding obtainedin the step (a), and disposing said shell layer molding so as to coatthe outer periphery of said core material molding obtained in the step(a); and (c) sintering said composite molding, wherein at least onepowder selected from the group consisting of oxides of metals of Groups4a, 5a and 6a of the Periodic Table, SiO₂, ZnO, and SnO₂ is subjected tocarbonization or nitriding before sintering or during the time ofsintering.
 35. The method according to claim 34 wherein said organicbinder is added in an amount of 30 to 70% by volume.
 36. The methodaccording to claim 34 wherein in the step (c), a heat treatment iscarried out at 1000 to 1500° C. for 0.5 to 5 hours in vaccum or inactiveatmosphere such that at least one powder selected from the groupconsisting of oxides of metals of Groups 4a, 5a and 6a of the PeriodicTable, SiO₂, ZnO and SnO₂ is subjected to carbonization or nitriding,followed by sintering at 1300 to 1900° C. for 0.5 to 5 hours in vaccumor inactive atmosphere.
 37. The method according to claim 34 wherein inthe step (c), at least one powder selected from the group consisting ofoxides of metals of Groups 4a, 5a and 6a of the Periodic Table, SiO₂,ZnO and SnO₂ is carbonized by reacting with the residual of said organicbinder used in the step (a).
 38. The method according to claim 34wherein said composite molding obtained in the step (b) is stretched byco-extrusion.
 39. The method according to claim 34 wherein saidcomposite molding of multi-filament structure is obtained by binding aplurality of said composite moldings stretched by co-extrusion, andperforming co-extrusion again.
 40. A method of manufacturing a compositeconstruction comprising the steps of: (a) forming a core materialmolding by mixing a mixture of at least one of carbide powder, nitridepowder and carbonitride powder selected from the group consisting ofmetals of Groups 4a, 5a and 6a of the Periodic Table, Si, Zn and Sn, aniron family metal oxide powder, and an organic binder, or a mixture ofat least one powder selected from the group consisting of oxides,carbides, nitrides and carbonitrdides of at least one selected from thegroup consisting of metals of Groups 4a, 5a and 6a of the PeriodicTable, Al, Si and Zn, a sintering additive powder containing an ironfamily metal oxide powder, and an organic binder, and then molding saidmixture in a continuous shape; (b) forming a composite molding byforming a shell layer molding having a different composition from saidmolding obtained in the step (a), and disposing said shell layer moldingso as to coat the outer periphery of said core material molding obtainedin the step (a); and (c) sintering said composite molding, wherein saidiron family metal oxide powder is subjected to reduction beforesintering or during the time of sintering.
 41. The method according toclaim 40 wherein said organic binder is added in an amount of 30 to 70%by volume.
 42. The method according to claim 40 wherein in the step (c),a heat treatment is carried out at 1000 to 1500° C. for 0.5 to 5 hoursin vaccum or inactive atmosphere such that said iron family metal oxidepowder is subjected to reduction, followed by sintering at 1300 to 1900°C. for 0.5 to 5 hours in vaccum or inactive atmosphere.
 43. The methodaccording to claim 40 wherein in the step (c), said iron family metaloxide powder is reacted with residual of said organic binder used in thestep (a), to oxidize said residual.
 44. The method according to claim 40wherein said composite molding obtained in the step (b) is stretched byco-extrusion.
 45. The method according to claim 40 wherein saidcomposite molding of multi-filament structure is obtained by binding aplurality of said composite moldings stretched by co-extrusion, andperforming co-extrusion again.